Arkansas weed control...

New grass herbicides for rice studied Last week I talked about one of our student projects - managing Hoelon-resistant ryegrass in wheat. This week, I'll discuss another student project. About the time we first looked at Ricestar, two other postemergence grass herbicides for rice (Clincher from Dow AgroSciences and Aura from BASF) were placed in our testing program.

Ron Talbert and I decided if all three herbicides were going to be developed simultaneously, we would need a dedicated effort to compare them. As I said last week, when you want a dedicated effort on something, you assign it to a student as a thesis project. In this case, we assigned it to Nathan Buehring, who came to our program from Mississippi State University. I went to school with Nathan's dad (as well as the father of Tom Barber, the student in the last article). You know you have the end of a career in sight when your students start coming from guys your age and younger.

There were several questions we wanted Nathan to get answered during the course of his project. We wanted a comparison of the relative effectiveness of the three herbicides on barnyardgrass, propanil-resistant barnyardgrass, broadleaf signalgrass and sprangletop.

In addition, we wanted to tie down specific rates for different grass sizes for each herbicide and grass.

We also wanted information about any potential antagonism or loss in grass activity when these herbicides are tank-mixed with broadleaf and/or sedge herbicides.

Nathan is now about to graduate, and he has done an outstanding job answering these questions, as well as providing us with a lot more information on these herbicides.

In general, all three herbicides effectively controlled all three grass species if applied at very early growth stages. However, the ability to control all three grasses over a range of sizes was somewhat disappointing.

The grass that was most difficult to control was barnyardgrass. Nathan found no control differences between propanil-resistant and susceptible barnyardgrass biotypes.

However, control of barnyardgrass with all three herbicides was poor once the barnyardgrass was beyond the three-leaf stage of growth. All three herbicides can do a nice job on the smaller grass.

On broadleaf signalgrass and Amazon sprangletop, Ricestar was the best herbicide across a range of growth stages, all the way to the preflood application. Clincher was weak on larger Amazon sprangletop and Aura was weak on larger broadleaf signalgrass.

We feel that any of these three herbicides that receive a label can help growers. However, you may be disappointed in their effectiveness on larger grasses, depending on the grass and the herbicide.

Of the three herbicides, applications of Aura resulted in the most cosmetic injury to the rice, and Clincher the least. Ricestar was in between, sometimes resulting in some slight yellowing of the rice that was quickly outgrown.

None of the herbicides caused any significant yield reduction due to the early injury.

As I understand it, federal label submissions are in for all three herbicides. None are expected to be granted in time for the 2001 use season. Since we have a large database with Ricestar, we are working with the Arkansas Plant Board to resubmit a Section 18 report.

I will touch on the tank-mix antagonism and some of the other things we have learned about these herbicides in future articles.